Gravimeters are used in geological exploration to measure the first derivatives of the earth's gravitational field. Whilst some advances have been made in developing gravimeters which can measure the first derivatives of the earth's gravitational field, because of the difficulty in distinguishing spatial variations of the field from temporal fluctuations of accelerations of a moving vehicle, these measurements can usually be made to sufficient precision for useful exploration only with land-based stationary instruments.
Gravity gradiometers (as distinct from gravimeters) are used to measure the second derivative of the gravitational field and use a sensor which is required to measure the differences between gravitational forces down to one part in 1012 of normal gravity.
A gravity gradiometer typically has a sensor in the form of at least one sensor mass that experiences a change in torque in response to a change in gravity gradient.
Gravity gradiometers have been used to attempt to locate deposits such as ore deposits including iron ore and geological structures bearing hydrocarbons. It would be convenient if gravity gradiometers could be positioned in aircrafts for such analyses. However, aircraft accelerations result in torques that are much larger that those associated with the gravity gradient. A reduction of an influence of such aircraft accelerations on the sensor provides a technological challenge.